1. Field of the Invention
The present invention relates to hydraulic cylinder devices and boat propelling apparatuses. More specifically, the present invention relates to a hydraulic cylinder device for use in adjusting a slant angle of the propelling apparatus main body, and a boat propelling apparatus including the hydraulic cylinder device.
2. Description of the Related Art
In boats equipped with a boat propelling apparatus, a slant angle of the propelling apparatus main body with respect to the boat body is adjusted in accordance with the mode of travel. Specifically, during a high speed travel mainly, the adjustment in the slant angle of the propelling apparatus main body is performed within a trim range, which is a range of small slant angles, for keeping an appropriate cruising attitude. During a slow speed travel or when the boat is stopping, the adjustment in the slant angle of the propelling apparatus main body is performed within a tilt range, which is a range of large slant angles, in order to prevent the propelling apparatus main body from hitting an underwater object. Such an adjustment of the slant angle of the propelling apparatus main body is performed, generally, by means of a power tilt and trim system.
For example, JP-A Hei 7-81678 discloses a hydraulic power tilt and trim system, in which a trim cylinder is slidably provided inside a tilt cylinder, and a piston rod is provided inside the trim cylinder. The piston rod has a tip connected with a swivel arm which is provided pivotably on the boat body, and a propelling apparatus main body is mounted on this swivel arm.
When adjusting the slant angle of the propelling apparatus main body in the trim range in this hydraulic power tilt and trim system, a hydraulic pressure in the tilt cylinder is adjusted in order to adjust the trim cylinder's position in the tilt cylinder. In this process, the piston rod moves (rises or lowers) inside the tilt cylinder together with the trim cylinder, and the swivel arm pivots with the piston rod as the rod rises or lowers. In this way, the adjustment is made of the slant angle of the propelling apparatus main body in the trim range. When adjusting the slant angle of the propelling apparatus main body in the tilt range, the trim cylinder is moved to its upper end of stroke in the tilt cylinder, and in this state, a hydraulic pressure inside the trim cylinder is adjusted. This adjusts the piston rod's position in the trim cylinder. In this process, the swivel arm pivots with the piston rod as the piston rod rises or lowers, adjusting the slant angle of the propelling apparatus main body in the tilt range.
In the hydraulic power tilt and trim system disclosed in JP-A Hei 7-81678, the piston rod moves linearly in an axial direction of the tilt cylinder and trim cylinder. On the other hand, the swivel arm is arranged to pivot with respect to the boat body. Because of this arrangement, there is a rubbing action where the piston rod's tip portion makes contact with the swivel arm. Specifically, the swivel arm rubs against the piston rod along a direction in which the piston rod travels. The rubbing action causes a sharp increase of a frictional force at a place of contact between the piston rod tip portion and the swivel arm, giving rise to a stick-slip phenomenon and an accompanying noise from the place of contact between the piston rod tip portion and the swivel arm.